The variety and use of electronic devices, especially portable electronic devices such as cellular telephones, laptop computers, and personal digital assistants (PDAs), has dramatically increased in recent years. With the increasing number and type of electronic devices, as well as communication formats between different electronic devices, the design of circuits in these electronic devices has become increasingly complex.
Many circuit designs used in electronic devices use integrated filters of various types to enable filtering of signals therethrough. In particular, multiple resistor-capacitor (RC) filters are often used within an integrated circuit. When fabricating the individual resistors and capacitors that form the RC filters, various processes are used. These processes include deposition of one or more metal and/or insulating layers used to form the resistor(s) and capacitor(s) as well as deposition of a photoresist layer, photolithography of the photoresist layer that defines the area of the deposited layer that will be used, etching of the deposited layer, removal of the remaining photoresist and cleaning of the substrate after the photoresist has been removed, among others.
However, variations exist between sets of processes. These variations originate from a variety of sources, such as differences in the thickness of the various layers deposited, the amount of misalignment of masks used during photolithography, etching times and etchant compositions for example. Thus, even though the same processes may be used to fabricate RC filters at different times on the same substrate or may be used to fabricate the same RC filter on different substrates, variations in the processes may cause the resistance and capacitance values of the filters to deviate by up to about 20% from the designed value, which causes the poles on the RC filter to deviate by twice that amount, by 40%. Moreover, since on-chip current sources use integrated resistors, these 20% resistance variations produce a similar variation in the absolute values of currents. Such a substantial deviation may cause significant operation problems unless the deviation is monitored and corrected for (essentially calibrated out) before the final product is shipped to a consumer. A similar deviation may exist over operational temperatures of the circuit, which also needs to be addressed.